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LC Chemistry > Experiments > Flashcards

Experiments Flashcards

1
Q

Prep of a solution

A

-rinse pipette, burette, w/ d.i water, and with solutions/chemicals

(if using powder/crystals )-weigh out solute on weighed clock glass, subtract mass of clock glass
-put into (clean) beaker, rinsing clock glass w/ d.i. beaker to ensure all solute goes into it (rinsings)
-stir, dissolve
-use funnel, pour into volumetric flask, rinsing again as you do so using d.i. water
/
(If using a solution)-fill pipette with pipette filler up to mark with the bottom of meniscus on the mark
-transfer into volumetric flask using a funnel, then rinse funnel to ensure all of the solution goes into it

  • fill up close to the mark with d.i. water, add final amount using dropper until bottom of meniscus on mark. Read at eye level.
  • stopper, invert several times to ensure solute uniform through solution
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2
Q

Iron tablet experiment - procedure for making up solution

A
  • crush tablets with mortar and pestle
  • washed into beaker
  • stirred to dissolve
  • transferred into flask using funnel
  • rinsings added to flask
  • add using dropper
  • top up carefully until bottom of meniscus level with mark
  • stopper, invert multiple times
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3
Q

iron tablet - why use dilute sulfuric acid in making up solution

A

to prevent air oxidation of Fe²⁺ in solution to Fe³⁺

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4
Q

iron tablet - why was more dilute sulfuric acid added before titration commenced?

A

to prevent formation of manganese(IV) (Mn⁺⁴) (brown precipitate) in solution

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5
Q

iron tablet - how was end-point detected?

A

colourles to pink

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6
Q

iron tablet - why nitric acid could not be used to provide acidic conditions for this reaction

A

nitric acid could not be used as it is a strong oxidising agent

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7
Q

measuring the heat of neutralisation (of ethanoic acid by sodium hydroxide) in the school laboratory

A
  • suitable container (polystyrene cup / calorimeter / glass vessel such as beaker) of known head capacity
  • known vols & concs of acid and base
  • measure initial temp, mix and note new (highest) temp
  • calculate heat produced using mcdeltatheta
  • calc for 1 mole H+ / calc heat of neutralisation
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8
Q

why ethanoic acid and sulfuric acid would have diff heats of neutralisation

A

sulfuric acid: strong acid - dissociated, present as ions, energy not needed to dissociate)

ethanoic acid: weak acid (undissociated, slightly dissociated, present as molecules, energy needed to dissociate)

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9
Q

water of crystallisation experiment - primary standard reagent which could have been used to standardise the HCL solution

A

anhydrous sodium carbonate

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10
Q

water of crystallisation experiment - suitable indicator, colour change,

A

methyl orange

yellow to red

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11
Q

water of crystallisation experiment - why not more than 1-2 drops of indicator should be used

A

methyl orange is a weak acid

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12
Q

describe the correct procedure for rinsing the burette before filling it with the solution to deliver + describe filling it

A

rinse with deionised water
rinse with solution

  • use funnel, pour in at top, take meniscus into account
  • remove funnel
  • ensure area below tap is filled
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13
Q

why is it important to fill the part below the tap of the burette?

A

air will be displaced by solution

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14
Q

describe procedure for weighing + making up solution from hydrated sodium carbonate crystals (for powders/crystals)

A
  • weigh on clock glass using electronic balance
  • transfer solution to beaker + rinse clock glass with d.i water using wash bottle to ensure all is transferred
  • dissolve in d.i water
  • transfer to volumetric flask using funnel + rinse with d.i water to ensure all is transferred
  • add d.i water to up to near mark on flask
  • add final amount using dropper, taking meniscus into account
  • stopper, invert several times
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15
Q

describe procedure for washing the pipette and using it to measure the solution

A

-rinse with d.i water, followed by solution

  • fill up to mark with pipette filler taking meniscus into account
  • transfer to flask with tip against side of flask to avoid splashing
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16
Q

three precautions with burette that should be taken in order to ensure an accurate measurement

A
  • vertical/read at eye level
  • add dropwise using dropper near end-point
  • rough titration first
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17
Q

sodium carbonate crystals, is not a primary standard but anhydrous sodium carbonate (Na₂CO₃) may be used as a primary standard. Why is this the case?

A
  • Na₂CO₃ is pure, stable, anhydrous (not hydrated), no water loss
  • solution of exact concentration can be made, no need to standardise by titration, any opposite point for sodium carbonate crystals
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18
Q

proceedure to measure out water from a beaker to a conical flask

A
  • rinse pipette with d.i water and then the water sample
  • use 25cm² pipette twice
  • read mark at eye level, bottom of meniscus on mark
  • touch tip against inside wall of conical flask, empty it out, do not blow out last drop from pipette
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19
Q

describe how the melting point of the crude product/recystallised product of benzoic acid could have been measured

A

-know diagram

  • sample on heating block
  • thermometer in melting block
  • block heated
  • note temp range over which sample melts
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20
Q

melting point benzoic acid experiment - two ways how you could conclude from melting points that the recrystallised product was purer than crude product

A
  • higher melting point
  • melting point closer closer to correct (in tables) value
  • sharper (narrower range)
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21
Q

one important use of benzoic acid or its salts

A
  • food preservative
  • disinfectant (antiseptic, fungicide)
  • calibration
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22
Q

describe the flame test

A
  • dip platinum wire in HCl to clean, clean if it does not change flame colour
  • dip in HCl
  • dip in sample of salt, sticks to wire
  • place salt in/over Bunsen flame
  • note colour of flame observed
  • if question specifies a salt, write the colour the flame should turn into
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23
Q

flame test - the metals and their colours

A

Barium nitrate: yellow-green

Copper sulfate: blue-green

Lithium carbonate: deep red

Potassium sulfate: lilac

Sodium sulfate: yellow

Strontium nitrate: red

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24
Q

flame test - why do metals give off a characteristic colour in a flame?

A

energy differences between energy levels in metal atoms vary from metal to metal. Using energy from flame, electrons move to higher energy levels then return to lower e levels, emitting light whos energies are equal to energy diff between higher e levels and lower e levels.

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25
Q

flame test - what procedure is used to avoid cross contamination?

A

Platinum wire: cleaned with concentrated HCL after each test

Wooden splint: diff splint used for each test

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26
Q

redox reactions of halogens - What is observed when chlorine gas is bubbled into an aqueous solution of sodium bromide? Explain your answer in terms of oxidation and reduction.

A

-solution turns red-brown

-bromide ions oxidised to bromide
Br⁻ –> Br₂

-chlorine reduced to chloride ions
Cl₂ –> Cl⁻

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27
Q

How do halogens react? + order of oxidising power

A

As oxidising agents, as they often react by taking an electron from another element.

F > Cl > Br > I > At

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28
Q

Why some halogens cant be used for the redox reaction

A
  • Fluorine extremely poisonous

- Astatine unstable + radioactive

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29
Q

Ethanoic acid in vinegar - measuring sample of vinegar and diluting it with d.i water

A
  • use pipette previously rinsed with deionised water and then rinsed with the vinegar solution it will contain
  • pipette: read at eye-level, bottom of meniscus on mark, don’t shake out/blow out last drop

-transfer to volumetric flask previously rinsed with deionised water, fill with d.i water until bottom of meniscus on mark (dropper at end), stopper + invert number of times

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30
Q

Ethanoic acid in vinegar - indicator

A

phenolphtalein

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31
Q

Ethanoic acid in vinegar - colour change at end point

A

pink to colourless

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32
Q

Ethanoic acid in vinegar - why vingar is diluted

A

to avoid small titre which would reduce accuracy of experiment

reduces amount of vinegar and amount of sodium hydroxide solution needed in experiment

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33
Q

Ethanoic acid in vinegar - why is phenolphthalein used as the indicator

A

this is a weak acid/strong base titration and phenolphthalein changes colour in appropriate pH range

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34
Q

why rough titration carried out first

A

to find approx endpoint, enables subsequent titrations to be carried out more quickly + more accurately

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35
Q

why are three accurate titrations carried out

A

reduce experimental error by calculating average value

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36
Q

when doing titration calculations, remember

A
  • dont use the first titration value given, as it is the rough titre unless stated that it is an accurate titre
  • get the average of the accurate titres
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37
Q

starting with solution of anhydrous sodium carbonate, what two titrations are required to standardise a sodium hydroxide solution?

A
  • anhydrous sod carbonate titrated with a strong acid (eg. HCl, sulfuric acid, nitric acid)
  • acid titrated with sodium hydroxide solution
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38
Q

what compound in white wine is converted to ethanoic acid in vinegar? what type of chemical process converts this compound to ethanoic acid?

A

ethanol

oxidation

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39
Q

name piece of equipment that should be used to measure x solution during the titration

A

burette

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40
Q

precaution that should have been taken as end point of titration approached + how it would have contributed to accuracy of titration result

A

-add drop by drop
(so end point will be precisely/accurately detected

-swirl flask contents
(ensure thorough mixing of reactants)

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41
Q

water of crystalisation in sodium carbonate - indicator

A

methyl orange

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42
Q

water of crystalisation in sodium carbonate - colour change

A

yellow to pink/peach

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43
Q

in acid-base titrations, why preferable to use little of indicator as possible

A

indicator is a weak acid/weak base, excessive use will affect titre value

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44
Q

physical appearance of hydrated sodium carbonate

A

white crystalline solid

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45
Q

explain water of crystallisation

A

water present in definite proportions in crystalline compounds

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46
Q

identify a primary standard reagent which could have been used to standardise the HCl solution

A

anhydrous sodium carbonate (Na₂CO₃)

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47
Q

potassium manganate(VII)/ammonium iron(II) sulfate titration - why ammonium iron(II) sulfate suitable as primary standard

A

it is stable + available in a highly pure form

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48
Q

potassium manganate(VII)/ammonium irom(II) sulfate titration - indicator + observation at end point

A
  • no indicator needed as manganate ions decolourised in reaction until end point
  • pale pink colourless remains
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49
Q

why pipette + burette rinsed with di water followed by a little of solutions they were to contain

A
  • di water washes out residual solutions in burette + pipette
  • remove any residual water so as to avoid dilution of solutions when they are added
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50
Q

why conical flask rinsed with d.i only

A

di water washes out any residual solution in flask, but if it was washed out with solution it was to contain, traces of it would remain + there would not be a precisely known amount of solution in flask

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51
Q

why you wash down sides of conical flask with di water from a wash bottle

A

ensure all of solution transferred

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52
Q

why washing down with di water does not affect results

A

only di water added, no extra reactants introduced

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53
Q

procedure used during titrations to ensure accuracy of end point

A
  • swirl flask while adding solution from burette
  • rinse down walls of flask with di water at intervals
  • add x dropwise as end point approached
  • read burette at eye-level
  • keep burette vertical
  • carry out rough titration first
  • use white tile to see colour changes in flask clearly
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54
Q

why are iron tablets sometimes medically prescribed?

A
  • to prevent anaemia

- for haemoglobin

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55
Q

iron in iron tablet - why potassium manganate(VII) must be standardised + why necessary to standardise immediately before use in titration

A
  • not primary standard
  • to find concentration
  • unstable
  • reacts with water
  • affected by light
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56
Q

iron in iron tablet - reagent used for standardising potassium manganate (VII)

A

ammonium iron(II) sulfate

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57
Q

iron in iron tablet - how solution prepared from iron tablets

A

-tablets crushed + dissovled
-transferred with rinsings to volumetric flask using funnel
-bottom of meniscus on mark
-dropper
-stopper + invert
etc

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58
Q

why more than one titration carried out

A

reduce experimental error by getting mean of accurate titres

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59
Q

steps taken to minimise error prior to titration

A
  • rinsed with di water

- rinsed with solution etc

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60
Q

iodine/thiosulfate titration - how iodine, a non-polar substance of very low water solubility, is brought into aqueous solution

A
  • reaction with potassium iodide (KI)

- forms soluble potassium triiodide (KI₃)

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61
Q

iodine/thiosulfate titration - indicator

A

starch solution

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62
Q

iodine/thiosulfate titration - when indicator is added

A

-when colour in conical flask is light/pale yellow (close to end point)

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63
Q

iodine/thiosulfate titration - colour change at end point

A

blue-black to colourless

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64
Q

iodine/thiosulfate titration - why using distilled water instead of di water would ensure a more accurate result

A

-di water could contain non-ionic substances that could be oxidised/reduced

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65
Q

iodine/thiosulfate titration - what must be added to bring iodine into aqueous soln?

A

-source of iodide ions (eg. potassium iodide)

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66
Q

iodine/thiosulfate titration - sequence of colours observed in flask from start of titration until end point

A
  • golden-brown colour
  • light/pale yellow
  • blue-black
  • colourless
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67
Q

iodine/thiosulfate titration - why hydrated sodium thiosulfate not suitable as primary standard

A
  • not stable

- loses water of crystallisation readily

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68
Q

iodine/thiosulfate titration - why iodine solutions made up using potassium iodide solution

A

iodine is a non-polar substance of very low water solubility

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69
Q

iodine/thiosulfate titration - why starch solution has to be freshly prepared + why added close to end point

A
  • it deteriorates quickly on standing

- to give sharp end-point

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70
Q

hypochlorite in bleach - indicator + when its added

A
  • starch solution

- when colour of solution in flash fades to pale yellow colour

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71
Q

what should be rinsed with di water and then with the solution

A

Di water: pipette, burette, conical flask

Solution: pipette, burette

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72
Q

hypochlorite in bleach - colour change at end point

A

blue-black to colourless

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73
Q

hypochlorite in bleach - colour when potassium iodide and sulfuric acid reaacted with the diluted bleach

A

reddish-brown / brown / red

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74
Q

hypochlorite in bleach - why excess potassium iodide used

A

so all bleach (hypochlorite) has reacted and to keep the iodine in solution

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75
Q

why stand the conical flask on white tile during titrations

A

so that colour-change (End point) clearer/more easily seen

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76
Q

why use volumetric flask instead of graduated cylinder

A

volumetric flask is quite an accurate measuring vessel while g cylinder is not

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77
Q

hardness of a water sample - solution titrated against sample to measure hardness

A

EDTA (ethylenediaminetetraacetic acid)

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78
Q

hardness of a water sample - why boiling + filtering sample would lower ppm

A

-temporary hardness was removed, only permanent hardness remaining

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79
Q

full name of EDTA

A

ethylenediaminetetraacetic acid

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80
Q

hardness of a water sample - indicator + colour change at end point

A
  • Eriochrome Black T

- wine red to blue

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81
Q

hardness of a water sample - purpose of buffer solutions

A

-to stabilise the pH of a solution

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82
Q

hardness of a water sample - buffer required for titration

A

-buffer solution of pH 10

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83
Q

hardness of a water sample - problem if wrong buffer was used

A
  • inaccurate end point

- edta complexing with other ions

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84
Q

hardness of a water sample - operations involving the flask carried out as edta being added from burette during titration

A
  • swirl flask o mix
  • wash down sides with di water
  • on white tile
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85
Q

hardness of a water sample - is the water having passed thru the deioniser suitable as di water in the lab?

A
  • not suitable
  • hardness remaining after passing thru deioniser
  • deioniser needs to be replaced
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86
Q

hardness of a water sample - purpose of adding buffer solution

A

keep pH at around 10 / ensure sharp end-point

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87
Q

hardness of a water sample - reaction of adding dilute HCl to deposit found on insides of kettles from hard water

A

CaCO₃ + 2HCl –> CaCl₂ + H₂O + CO₂

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88
Q

dissolved oxygen by redox titration - why avoid trapping air bubbles each time stopped inserted into sample and when ussing dropper

A

would increase dissolved oxygen / oxygen concentration

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89
Q

dissolved oxygen by redox titration - solutions added to sample

A
  • manganese(II) sulfate solution
  • alkaline potassium iodide

-concentrated sulfuric acid

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90
Q

dissolved oxygen by redox titration - observation after adding sulfuric acid + mixing contents of bottle

A

brown solution

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91
Q

dissolved oxygen by redox titration - conclusion reached if a white precipitate observed instead of brown precipitate after first two additions of reagents to bottle filled with river water

A

extremely low oxygen in water

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92
Q

dissolved oxygen by redox titration - why is immediate determination of dissolved oxygen considered best practice

A

biochemical reactions occur / action of micro-organisms

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93
Q

dissolved oxygen by redox titration - why analyse sample of river water immediately?

A
  • so oxygen content doesnt increase due to photosynthesis

- so oxygen content doesnt change due to activity of organisms in water

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94
Q

dissolved oxygen by redox titration - in making additions to sample, why should solutions be concentrated?

A

-minimise change in oxygen dissolved in sample / so small volume (amount) supplies excess

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95
Q

dissolved oxygen by redox titration - how addition of conc solution of manganese(II) sulfate should be carried out

A
  • additions made so water overflows from bottle
  • make additions under level of the water
  • using dropper
  • do not bubble air (oxygen) into water in process
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96
Q

dissolved oxygen by redox titration - precautions when replacing stopper after each addition

A

-do not trap air (oxygen) bubbles

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97
Q

dissolved oxygen by redox titration - indicator + when it should be added + colour change at end point

A
  • starch solution
  • when solution is pale yellow
  • blue black to colourless
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98
Q

dissolved oxygen by redox titration - why bottles shaken

A

help dissolved oxygen to react

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99
Q

dissolved oxygen by redox titration - why bottles are completely filled

A

prevent additional oxygen from air dissolving in water

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100
Q

dissolved oxygen by redox titration - why bottle stored in dark

A

prevent oxygen production by photosynthesis

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101
Q

why conical flask instead of beaker

A

allow easy mixing of contents by swirling

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102
Q

why funnel removed from burette after adding acid solution

A

so drops of solution from funnel will not fall into burette

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103
Q

why clamp burette vertically?

A

enable liquid level to be read correctly

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104
Q

how liquid level in burette adjusted to zero mark

A
  • fill to below mark + add dropwise

- bottom of meniscus on mark

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105
Q

why pipette filler used to fill pipette with solution

A

safety/hygiene

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106
Q

standardisation of HCl using standard soln of sodium carbonate - indicator + colour change at end point

A

methyl orange

yellow to red

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107
Q

test for carbonate anions

A
  • add HCl solution
  • effervescence, colourless gas evolved
  • limewater test: becomes milky, CO₂ evolved
  • Add magnesium sulfate, white precipitate formed
  • heated, no change
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108
Q

test for hydrogencarbonate anions

A
  • add HCl solution
  • effervescence, colourless gas evolved
  • limewater test: becomes milky, CO₂ evolved
  • Add magnesium sulfate, no change
  • heated, white precipitate appears
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109
Q

test for sulfate anions

A
  • Add barium chloride, white precipitate formed

- add HCl solution, no change

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110
Q

test for sulfite anions

A
  • add barium chloride, white precipitate formed

- add HCl solution, white precipitate disappears

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111
Q

test for nitrate anion

A
  • add iron(II) sulfate
  • nothing observed
  • add concentrated sulfuric acid
  • brown ring appears at boundary between liquid layers
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112
Q

ethyne - What is in each piece of equipment?

A
  • water dropped onto calcium carbide (in reaction flask)
  • acidified copper(II) sulfate solution in another tube
  • water in water bath
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113
Q

ethyne - observation in reaction flask as water dropped onto calcium carbide

A

-turns milky / bubbling / effervescence (fizzing)

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114
Q

ethyne - why first few test tubes of gas collected were discarded

A

-contain air (nitrogen, oxygen, argon, carbon dioxide)

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115
Q

ethene, ethane, ethyne diagrams

A

know diagrams from notes

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116
Q

precautions when carrying out ethene experiment

A
  • remove delivery tube from water before removing heat at end to avoid suckback into hot test-tube
  • keep ethanol away from flame - ethanol flammable
  • keep long hair tied back/wear gogles/wear gloves - avoid burns/contact with chemicals
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117
Q

ethene, ethyne experiments diagrams

A

know diagrams from notes

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118
Q

precautions when carrying out ethene experiment

A
  • remove delivery tube from water before removing heat at end to avoid suckback into hot test-tube
  • keep ethanol away from flame - ethanol flammable
  • keep long hair tied back/wear gogles/wear gloves - avoid burns/contact with chemicals
  • wear mask - avoid inhaling glass wool
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119
Q

reagent used to test gases for unsaturation

A

Bromine (Br₂) solution

120
Q

reagent used to test gases for unsaturation

A

Bromine (Br₂) solution / Bromine water

Acidified potassium manganate(VII)

121
Q

ethyne - appearance of calcium carbide

A

black/dark/grey

122
Q

saturation test for gas

A
  • bubble ethene/ethyne into bromine water

- red (brown/orange) bromine solution decolourises

123
Q

saturation test- ethene

A

-colour of bromine water changes from red to colourless

or

-purple colour changes to colourless (potassium manganate(VII)

124
Q

saturation test - ethyne

A

-bromine water changes from red to colourless

or

–purple colour changes to colourless (potassium manganate(VII)

125
Q

major use of ethene

A

-manufacture of polythene

126
Q

major use of ethyne

A
  • cutting metals
  • welding metals
  • make ethanal
127
Q

major use of ethyne

A
  • cutting metals
  • welding metals
  • make ethanal
128
Q

organic product of adding bromine water to ethyne

A

dibromoethene or tetrabromoethane

129
Q

describe how to test samples x and y for unsaturation

A
  • Add bromine water
  • decolourises if unsaturated
  • no change in colour if saturated
130
Q

ethene - what is in each piece of equipment?

A
  • glass wool with ethanol in tube

- aluminium oxide in tube over flame

131
Q

ethene - what stage is suck-back likely to occur?

A

when heat is removed at the end

132
Q

ethene - consequence of suck-back occurring

A

cold water sucked into test tube, causing test tube to crack

133
Q

ethene - how to avoid suckback

A

-remove delivery tube from water before removing heat

134
Q

ethene - colour of aluminium oxide

A

white powder/solid

135
Q

ethene - type of reaction in preparation of ethene

A

elimination

136
Q

Which evaporates more quickly, ethanal, ethanoic acid, or eugenol?

137
Q

ethanal - chemical test to confirm ethanal can be easily oxidised / test for ethanal

A
  • Add Fehling’s solution / Tollens’ reagent
  • heat gently
  • Fehling’s solution: red/brown precipitate formed. / Tollen’s reagent: slver mirror formed
138
Q

what happens when you add water to eugenol and shake it vigorously?

A

white emulsion formed

139
Q

what happens when you add water to ethanoic acid?

A

colourless solution observed

140
Q

observation after adding cyclohexane to eugenol

A

two layers

-organic (cyclohexane) layer and aqueous layer

141
Q

ways to test for ethanoic acid

A
  • odour
  • universal indicator paper
  • magnesium strip
  • anhydrous sodium carbonate
  • ethanol with concentrated sulfuric acid
142
Q

ethanoic acid - odour

A

vinegar odour

143
Q

ethanoic acid - universal indicator paper

A

changes colour from green to red - solution is acidic

144
Q

ethanoic acid - magnesium strip

A

effervescence - hydrogen gas generated

145
Q

ethanoic acid - anhydrous sodium carbonate

A

effervescence - carbon dioxide gas generated

146
Q

ethanoic acid - ethanol with concentrated sulfuric acid

A

sweet odour and oily droplets - ethyl ethanoate produced

147
Q

colour change in oxidation of ethanol to ethanal

A

orange to green

148
Q

test to see if organic product is an aldehyde

A

use ethanol tests

fehling’s solution/tollens’ reagent

149
Q

ethanoic acid - what is in what

A
  • ethanol and water in tap funnel

- sodium dichromate, water, sulfuric acid, boiling chips in flask that is in water bath over hot plate

150
Q

ethanoic acid - precautions to avoid excessive heat production during addition experiment

A
  • add in small quantities (dropwise)
  • shake (stir) after each addition
  • cool reaction vessel
151
Q

ethanoic acid - colour change as ethanol was oxidised

A

orange to green

152
Q

ethanoic acid - purpose of heating the reaction mixture under reflux after addition from tap funnel was complete

A
  • to speed up reaction
  • ensure complete oxidation
  • heat without loss of vapour
153
Q

ethanoic acid - how ethanoic acid product was isolated from reaction mixture

A

isolated by distillation

154
Q

ethanoic acid - diagram of oxidising ethanol into ethanoic acid

A

2007 q2 diagram

155
Q

ethanoic acid - observation of adding solid sodium carbonate to ethanoic acid

A

effervescence/fizzing/bubbling

156
Q

free chlorine in swimming pool - reagents used to detect free chlorine + colour observed when it reacts with free chlorine

A

potassium iodide (KI) and ethanoic acid

orange

157
Q

free chlorine in swimming pool - how a colorimeter could be used to estimate concentration of free chlorine in a sample

A
  • prepare a number of standard solutions of reagent
  • place in calorimeter + note colorimeter readings
  • plot graph of concentration vs readings
  • get concentration (ppm) of sample from graph using sample absorbance
158
Q

free chlorine in swimming pool - problem if free chlorine level too low

A

-infection (disease)

159
Q

free chlorine in swimming pool - problem if free chlorine level too high

A
  • unpleasant smel
  • eye/skin irritation
  • taste impared
160
Q

example of a free chlorine species in swimming pool water

A

Chlorine (Cl₂)

161
Q

why is the level of free chlorine higher in swimming pool water than in drinking water

A
  • to kill pathogens/harmful bacteria added by swimmers
  • swimming pool water more contaminated
  • higher level would b dangerous to drink/give bad taste to drinking water
162
Q

describe how the concentration of suspended solids could be measured in a sample

A
  • known volume of water sample through weighed filter paper
  • dry filter paper
  • find new mass of filter paper and residue (reweigh)
  • calculate mass of reside by subtracting mass of filter paper
163
Q

free chlorine - why potassium iodide used

A

it is readily oxidised to iodine by chlorine

164
Q

free chlorine - why ethanoic acid used

A

to ensure all of the chlorine reacts and that all of the iodine formed dissolves

165
Q

free chlorine - advantage of using colorimeter to determine chlorine

A

reading can be taken very quickly

166
Q

determination of pH of a water sample

A

use pH mater or pH paper

167
Q

determination of total dissolved solids using evaporation

A
  • evaporate known volume of filtered water sample in weighed beaker
  • reweigh afterwards
168
Q

relative molecular mass of volatile liquid - diagram of apparatus

169
Q

relative molecular mass of volatile liquid - example of a liquid suitable for use in this experiment

A

propanone (acetone) (56 degrees celsius)

170
Q

relative molecular mass of volatile liquid - how mass of vapour determined

A
  • weigh flask
  • heat until all liquid gone (until vaporised), cool ,dry and reweigh
  • mass is the difference
171
Q

relative molecular mass of volatile liquid - how volume of vapour determined

A

-fill flask with water and empty into graduated cylinder

172
Q

relative molecular mass of volatile liquid - why pressure of vapour is same as atmospheric pressure

A

-the pinhole means that vapour is exposed to the air
/
-vessel is open to atmosphere

173
Q

relative molecular mass of volatile liquid - why is this method unsuitable for non-volatile liquids?

A

-they do not vaporise easily, boiling points are too high

174
Q

relative molecular mass of volatile liquid - modern intrumental technique to measure relative molecular masses of liquids, solids, and gaseous substances

A

mass spectrometer

175
Q

volatile liquid definition

A

easily vaporised/easily changed to gas

176
Q

relative molecular mass of volatile liquid - proceedure of experiment

A
  • diagram
  • flask, sealed with foil with small hole, immersed so at least half is under water
  • describe how mass, volume, and temp measured
177
Q

relative molecular mass of volatile liquid - how temp of sample measured

A

-use thermometer to read temperature of water

178
Q

relative molecular mass of volatile liquid - how may the pressure be measured?

179
Q

re-crystallisation of benzoic acid + melting point - diagram

180
Q

re-crystallisation of benzoic acid + melting point - describe a method to measure the melting point of benzoic acid

A
  • sample on aluminium block shown in diagram, thermometer in melting block
  • heat block slowly with bunsen burner
  • note temperature range at which melting occurs (temperature measured on thermometer)
181
Q

re-crystallisation of benzoic acid + melting point - The melting-point range of F is lower and broader than that of G. Which is the purer benzoic acid sample?

A

G.

F is less pure

182
Q

re-crystallisation of benzoic acid + melting point - lab technique that could be used to purify impure benzoic acid

A

recrystallisation

183
Q

re-crystallisation of benzoic acid + melting point - way of maximising yield of recrystallisation process

A
  • use minimum amount of solvent (water)
  • cool fully
  • avoid crystallisation during hot filtration
184
Q

re-crystallisation of benzoic acid + melting point - how would recrystallisation have affected the melting point range?

A
  • melting point range sharper (narrowed, smaller)
  • melting point raised
  • melting point closer to correct (in tables) value
185
Q

re-crystallisation of benzoic acid + melting point - solvent used for recrystallisation + why its suitable

A
  • solvent: water

- very soluble in hot but slightly less soluble in cold

186
Q

what solids are collected in filtration paper?

A

insoluble solids

187
Q

re-crystallisation of benzoic acid + melting point - where is the benzoic acid collected?

A

the second filtration after the crystallisation, which is after the hot filtration

188
Q

re-crystallisation of benzoic acid + melting point - how could benzoic acid be separated from salt during the procedure?

A
  • both soluble in hot water

- benzoic acid less soluble in cold water so crystalises out of solution while NaCl remains in solution

189
Q

re-crystallisation of benzoic acid + melting point - steps

A
  1. dissolving
  2. hot filtration
  3. crystallisation
  4. filtration
  5. drying
190
Q

re-crystallisation of benzoic acid + melting point - how benzoic acid was dried

A
  • warm place
  • dry in warm oven
  • air drying (eg. leave on filter paper/on a radiator)
191
Q

re-crystallisation of benzoic acid + melting point - how melting point of two diff samples differ

A
  • impure lower melting point
  • impure less sharp range
  • recrystallised closer to correct value
  • recrystallised sharper (narrower range)
192
Q

use of benzoic acid

A

food preservative

disinfectant

193
Q

re-crystallisation of benzoic acid + melting point - why use minimum amount of hot water

A

to maximise yield / so crystals will form on cooling

194
Q

re-crystallisation of benzoic acid + melting point - when insoluble impurities were removed + how

A
  • filtration of hot solution / first filtration

- remained on filter paper

195
Q

re-crystallisation of benzoic acid + melting point - when soluble impurities removed + how

A
  • filtration of recrystallised benzoic acid

- stayed in solution

196
Q

re-crystallisation of benzoic acid + melting point - how to ensure recrystallisation was complete

A

cool fully

197
Q

heat of reaction of hydrochloric acid with sodium hydroxide - suitable material for reaction vessel to avoid heat loss to surroundings

A

polystyrene
styrofoam
plastic
cardboard

198
Q

advantage of using burette instead of grad cylinger for measuring

A

more accurate

199
Q

disadvantage of using burette instead of grad cylinder for measuring

A

slow addition

200
Q

heat of reaction of hydrochloric acid with sodium hydroxide - ways of ensuring rise in temp measured as accurately as possible

A

sensitive thermometer used

avoid splashing

201
Q

heat of reaction of hydrochloric acid with sodium hydroxide - hazards associated with solutions used

A

corrosive / burns skin / damages eyes

202
Q

warning symbols

A

know how to draw warning symbols!

203
Q

heat of reaction of hydrochloric acid with sodium hydroxide - experimental problem if 0.1M NaOh and 0.1M HCl used instead of 1.0M solns

A

very small temp rise

greater percentage error

204
Q

heat of reaction of hydrochloric acid with sodium hydroxide - precaution when handling solutions

A

do not allow contact with skin, wear protective clothing (gloves, labcoat)

205
Q

heat of reaction of hydrochloric acid with sodium hydroxide - how initial temp of reaction mixture could have been obtained if they were stored at diff temps

A

get average temps of two solutions
or
wait until both solutions at same temp

206
Q

heat of reaction of hydrochloric acid with sodium hydroxide - three precautions taken to obtain accurate value for highest temp teached by reaction mixture

A
  • sensitive thermometer
  • add quickly
  • add without splashing
  • replace cover quickly
  • stir constantly
207
Q

heat of reaction of hydrochloric acid with sodium hydroxide - why use a polystyrene foam cup

A

its a good insulator/prevents heat loss

208
Q

piece of equipment used in industry to measure heats of combustion

A

bomb calorimeter

209
Q

rate of production of oxygen from hydrogen peroxide - diagram

210
Q

decomposition - which run completed first and which had slower initial rate?

A

completed first: whatever stopped increasing in volume faster

slower initial rate: whatever stopped increasing in volume later

211
Q

rate of production of oxygen from hydrogen peroxide - catalysis involved in reaction

A

surface adsorption

212
Q

rate of production of oxygen from hydrogen peroxide - how catalyst could differ in diff runs

A

greater surface area / purer (for faster initial rate)

213
Q

rate of production of oxygen from hydrogen peroxide - warning symbol put on hydrogen peroxide

A

circle with flames rising

214
Q

rate of production of oxygen from hydrogen peroxide - why graph is steepest at beginning

A

greatest rate

215
Q

rate of production of oxygen from hydrogen peroxide - finely powdered vs coarsely powdered - which would have greater average rate of reaction? + why

A
  • finely powdered

- greater activity/greater surface area available

216
Q

rate of production of oxygen from hydrogen peroxide - change in graph if concentration of solution was lower

A

-rise less steep

217
Q

benzoic acid from phenylmethanol - appearance of phenylmethanol at room temp

A

colourless / pale yellow

218
Q

benzoic acid from phenylmethanol - colour change when phenylmethanol heated gently with potassium manganate(VII) solution

A

purple to dark brown

219
Q

benzoic acid from phenylmethanol - substances added to allow separation of benzoic acid from other substances after oxidation was complete

A

Hydrochloric acid (HCl)

Sodium sulfite (Na₂SO₃)

220
Q

benzoic acid from phenylmethanol - changes observed in reaction vessel after addition of two substances and as cooling occured

A

mixture decolourises

221
Q

benzoic acid from phenylmethanol - changes in oxidation number of manganese during experiment

A

7 to 4 to 2

222
Q

separation of a mix of indicators using chromatography - diagram

A

diagram (paper chromatography or thin-later chromatography)

223
Q

define inmiscible liquids

A

do not mix

224
Q

prep of soap - stages

A
  • stage 1 - refluxing
  • stage 2 - distillation
  • stage 3 - washed into beaker containing brine
  • stage 4 - filtration to isolate soap
225
Q

prep of soap - purpose of refluxing in stage 1

A
  • allow time for reaction / bring reaction to completion

- without losing volatile material/without flask boiling dry

226
Q

prep of soap - type of reaction in refluxing

A

saponification

227
Q

prep of soap - substance removed by distilation

228
Q

prep of soap - function of brine

A

to precipitate the soap / soap insoluble in brine

229
Q

prep of soap - why wash soap thoroughly in last stage

A

remove sodium hydroxide, which could burn skin when soap used

230
Q

prep of soap - how to wash the soap

A

brine (salt solution) / ice-cold water

231
Q

prep of soap - what is the co-product of the reaction? where was it located at the end of the process?

A

glycerol/glycerine **know how to draw molecule

in brine/filtrate

232
Q

prep of soap - how a soap can dissolve both non-polar oils and ionic salts in sweat

A

C₁₇H₃₅ is non-polar and dissolves oils

-COO⁻Na⁺ attracted to salts in sweat

233
Q

IUPAC name for glycerol

A

propane-1,2,3-triol

234
Q

prep of soap - purpose of ethanol

235
Q

prep of soap - diagrams

236
Q

prep of soap - how ethanol removed after reflux stage

A

diagram of distillation

237
Q

prep of soap - how soap isolated from other subtstances left in reaction mixture

A
  • add in a little boiling water
  • reaction mixture added to brine
  • precipitated soap got by filtration
  • wash with more brine
238
Q

prep of soap - how soap purified + dried

A

purified: wash with brine
dried: warm place / oven / air dry

239
Q

prep of soap - why remove ethanol after reflux

A

easier to isolate soap

soap contaminated with ethanol

240
Q

prep of soap - location of excess sodium hydroxide

A

in filtrate/brine

241
Q

observation of adding soap in di water

242
Q

observation in adding soap to mineral water from a limestone region

243
Q

chemical difference between vegetable and animal fats

A

animal saturated

vegetable unsaturated

244
Q

prep of soap - what should be added to reaction flask prior to reflux?

A
  • lard
  • sodium hydroxide
  • ethanol
  • anti-bumping agent
245
Q

prep of soap - why a minimum of hot water used to dissolve residue from distillation

A
  • maximise soap precipitation out

- to minimise soap remaining dissolved

246
Q

prep of soap - what is brine?

A

salt solution

247
Q

prep of soap - how soap could be isolated from brine _

248
Q

prep of soap - precaution to ensure soap is free of sodium hydroxide

A

wash with brine

249
Q

natural product you extract using steam distillation

A

clove oil (eugenol)

250
Q

during reflux - what happened to liquid in flask during reflux?

A

hot vapour rose and was condensed (returned to flask)

251
Q

refluxing - how did refluxing this mixture help bring reaction to completion?

A

allowed enough time to bring reaction to completion

heating without loss of reactants

252
Q

extraction of clove oil from cloves - appearance of material collected during steam distillation

A

cloudy / milky liquid

mixture of clove oil and water

253
Q

extraction of clove oil from cloves - what distilled across along with the product?

254
Q

extraction of clove oil from cloves - safety feature of steam distillation apparatus

A
  • safety tube/steam tube: releases pressure/steam, preventing explosion
  • air-tight seals: no steam escapes, preventing burns
255
Q

substance you isolated by steam distillation + plant it was extracted from

A

clove oil from cloves

256
Q

extraction of clove oil from cloves - function of safety tube (above flask)

A
  • release of pressure
  • prevents build up of steam
  • avoids explosion
257
Q

extraction of clove oil from cloves - technique to separate clove oil from water (liquid-liquid extraction of clove oil)

A

shake with suitable solvent (eg. cyclohexane)

258
Q

use of clove oil

A

flavouring / seasoning / used in food

259
Q

why clove oil cannot be distilled directly from cloves

A

clove oil contains component molecules whose boiling points are very high

260
Q

effect on reaction rate of concentration and temp - method you could use to determine whether the same mass of x had been formed in each run

A
  • cross under flask
  • obscured
  • when viewed through same depth of solution in each run
261
Q

effect on reaction rate of concentration and temp - how to investigate effect of changing temp on reaction rate

A
  • heat solutions using water baths/hot plate
  • with fixed volumes and concetrations of sodium thiosulfate and HCl
  • record reaction times
262
Q

effect on reaction rate of concentration and temp - change observed in conical flask during reaction

A
  • cloudiness

- due to formation of sulfur

263
Q

effect on reaction rate of concentration and temp - how observed changed used to obtain reaction times

A
  • stand flask on cross

- note time when cross becomes invisible

264
Q

effect on reaction rate of concentration and temp - effect on experiment if lower molarity of solution used

A

-reaction slower

bc rate directly proportional to thiosulfate concentration

265
Q

effect on reaction rate of concentration and temp - describe how you would measure the reaction time when hcl and sodium thiosulfate react

A
  • place thiosulfate soln in a vessel over a cross on a white surface
  • add HCl and start a stopwatch/timer
  • note time when cross becomes invisible when viewed thru solution
266
Q

effect on reaction rate of concentration and temp - describe how you would show rate of this reaction is directly proportional to conc of sodium thiosulfate solution

A
  • repeat procedure for each solution
  • find reciprocals of the times (1/t values) to get the rates
  • plot 1/t against concentration
  • plot of rate against concentration gives a straight line through the origin
267
Q

effect on reaction rate of concentration and temp - precipitate produced in each flask

268
Q

effect on reaction rate of concentration and temp - why conc and volume of HCl kept constant

A

so only one variable is changed

269
Q

effect on reaction rate of concentration and temp - would you expect reaction times to increase or decrease as temp increased?

A

decrease

reaction rate increases with temperature

270
Q

effect on reaction rate of concentration and temp - why reciprocal of the time used as measure of initial rate of reaction

A

rate and time inversely related

rate ∝ 1/t

271
Q

refluxing - glasssware used at the top

272
Q

what is an emulsion?

A

oil droplets in water

273
Q

clove oil - safety precaution when using separating funnel

A

work in fume cupboard

avoid flame

274
Q

clove oil - how clove oil isolated following liquid-liquid extraction

A

evaporate solvent/distil

275
Q

benzoic acid - why you woildn’t need to carry out a hot filtration (2018)

A

no insoluble impurities

276
Q

benzoic acid - advantage of suction filtration over gravity filtration

A

faster / helps dry the crystals

277
Q

benzoic acid - how you oculd verify recrystallised b acid was purer

A

-measure melting points of both samples
-purer: melting point closer to correct value
-impure: melting point …
etc

278
Q

heat of reaction - why stir

A

distribute heat evenly

279
Q

heat of reaction - why temp begins to fall gradually later

A

heat loss to surroundings

280
Q

heat of reaction - why use moderately concentrated solns instead of dilute solns

A

bigger temp rise recorded

less percentage error

281
Q

heat of reaction - how you could get a more accurate result

A
  • use insulation: stops heat loss to surroundings

- use acids and bases with greater concs: greater temp rise

282
Q

another organic compound that could be formed when ethanol is oxidised using acidified sodium dichromate

A

ethanoic acid / acetic acid

283
Q

benzoic acid from phenylmethanol - explain colour change by reference to transition metal reagent used

A

MnO4^- changes to Mn^2+

284
Q

Experiment: water hardness - rectifying splash of solution up side of conical flask + why

A

side of flask washed down with d.i. water

-doesn’t affect concentration of reactants in flask as it contains no ions

285
Q

Experiment: water hardness

solution added before titration proceeds + purpose

A
  • pH 10 buffer solution
  • added before titration proceeds
  • keeps the pH at about 10, ensuring necessary conditions for effective operation of indicator are maintained
286
Q

Experiment: water hardness - effect of boiling the water

A

the titre would be smaller as boiling removes temp hardness

287
Q

iron tablet calculations - finding mass of iron in one tablet from concentration of iron in solution

A
  • When you get the molarity, convert it from mol/L to mol/volume of soln (eg. 250 cm3),
  • then use that value in n=m/mr to get the number of moles for 4 tablets
  • then divide by 4 to get mass for one tablet
288
Q

finding the number of moles of something

A

find the no of moles of the thing added from the burette, and the no of moles in the flask should be either the same or different (check mole ratio on balanced equation)

289
Q

percentage yield questions

A

check question to see what they want you to use for percentage yield, eg “what is the percentage yield, in mass?” find mass then use those to get the % yield

290
Q

Find no of moles when given grams of a crystal

A

Convert the mass to per litre first,
eg. “8.82g used, diluted to 250cm3 solution”, this is 8.82g/250 cm3, however to use the n=m/mr formula, we must convert to per litre so multiply 8.82 by 4 first

291
Q

water of crystallisation - x , getting a decimal

A

round up or down if you get a decimal or write it exactly as you get it

292
Q

finding Mr (when you see moles on equation)

A

when finding Mr, ignore the mole in front of the chemical formula (eg. 3NaOH, just find Mr of NaOH, not 3NaOH)

293
Q

heat of neutralisation - finding heat change when given temps of the acid and base, and highest temp recorded

A
  • find average temp between acid and base (a + b/2)
  • find temp change by doing highest temp - average temp of acid and base
  • use heat formula
294
Q

finding Mr - values to use

A

use the values given on the front of the paper

295
Q

soap equation

A

learn off soap equation on sheet

296
Q

describe how you would demonstrate the effects of particle size on rate

A
  • mass of small particles equal mass of larger particles
  • added to equal volumes of HCl of same conc
  • note times to complete reactions

LC Chemistry (26 decks)

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